A known examples of devices for reading a paper sheet medium include a magnetic sensor device including a magnet and a magnetic sensor to read a magnetic pattern of a magnetic component, such as a magnetic ink, formed on a medium, such as a banknote. A magnetoresistive element (see, for example, Patent Literature 1) or a Hall device is used for a detection by the magnetic sensor.
A magnetic sensor device described in Patent Literature 1 includes a magnet and a magnetoresistive element. The magnet faces one surface of a paper sheet medium containing a magnetic component, and has different magnetic poles in a vertical direction perpendicular to the transport direction of the paper sheet medium, forming a cross magnetic field intersecting with a sensing target. The magnetoresistive element is located between one magnetic pole of the magnet forming a cross field and the paper sheet medium, and outputs, as a change in a resistance value, a change in the component of the cross field in the transport direction due to the magnetic component of the paper sheet medium that is transported in the cross magnetic field. The magnetoresistive element is located between the both ends of one magnetic pole of the magnet in the transport direction, and the magnetoresistive element is arranged such that the magnetoresistive element is deflected in the transport direction from the center of the length of one magnetic pole of the magnet in the transport direction.
A magnetic sensor device in another form described in Patent Literature 1 includes a magnetic circuit and a magnetoresistive element. The magnetic circuit faces one surface of a sensing target containing a magnetic component, and forms a cross magnetic field intersecting with the sensing target between a central portion of the magnetic circuit and yokes located upstream and downstream relative to the central portion in the transport direction of the sensing target. The magnetoresistive element is located between the sensing target and the central portion, and outputs, as a change in a resistance value, a change in the component of the cross magnetic field in the transport direction due to the magnetic component of the sensing target that is transported in the cross magnetic field. The magnetoresistive element is located between the both ends of the central portion in the transport direction, and the magnetoresistive element is arranged such that the magnetoresistive element is deflected in the transport direction from the center of the length of the central portion in the transport direction.
Another magnetic sensor device includes a magnetic shield to avoid leakage of a magnetic field and influence of external factors (e.g., Patent Literature 2 and Patent Literature 3). Another magnetic sensor device includes a shield cover that transmits a magnetic field for electrical shielding (e.g., Patent Literature 4). Another magnetic sensor device includes an outer shell that serves as a shield cover (e.g., Patent Literature 5 and Patent Literature 6).
The magnetic sensor device described in Patent Literature 2 includes a magnetoresistive element fixed to an upper surface of a magnetic material board and a permanent magnet fixed to a lower surface of the magnetic material board, and, in Patent Literature 2, a magnetic shield unit having the ends protruding upward is disposed under the permanent magnet. The magnetic sensor device described in Patent Literature 3 has a magnetic material formed around a magnetic sensor unit including a magnetoresistive element and a magnetic field generator. The magnetic material formed around the magnetic sensor unit serves as a magnetic shield.
The magnetic sensor device described in Patent Literature 4 has different magnetic poles in a vertical direction perpendicular to the transport direction of a paper sheet medium containing a magnetic component. Also, the magnetic sensor device described in Patent Literature 4 includes a magnet extending in a longitudinal direction perpendicular to the transport direction and anisotropic magnetoresistive elements. The anisotropic magnetoresistive elements are linearly arranged in the longitudinal direction. The magnet is characterized in that the length of the magnet in the vertical direction in an end in the longitudinal direction of the magnet is larger than the vertical length of the magnet in a central portion in the longitudinal direction of the magnet.
In the magnetic sensor device described in Patent Literature 4, the length of the magnet in the vertical direction at the end is larger than the length of the magnet in the vertical direction at the central portion, where the vertical direction is perpendicular to the transport direction, so that a bias magnetic flux can be forcibly applied in the same non-magnetosensitive direction (longitudinal direction) of the anisotropic magnetoresistive elements that are implemented by arranging the anisotropic magnetoresistive elements in the linearly arrangement direction. As stated therein, the anisotropic magnetoresistive elements can output signals of the same level in a stable manner even for a magnetic pattern tilted in a planar direction.
The magnetic sensor device described in Patent Literature 5 includes a magnet extending in a longitudinal direction, magnetoresistive elements, and a shield cover extending in the longitudinal direction, wherein the magnet and the magnetoresistive element are contained in or held by a housing and the shield cover is fixed to the housing. The magnetic sensor device described in Patent Literature 6 has a cover fixed with an adhesive for protecting magnetoresistive elements.